How to create a semi transparent plastic shader?
There are elements of Refraction, Glossy, and Subsurface scattering in there so how about something like this :



This produces the following :



Vary the Mix factors, roughness and Subsurface scale to get the desired effect. Don't forget to have something in the scene to reflect/refract - eg, world environment texture and/or patterned surface, and suitable lighting, etc. Also, bevel any edges and ensure to add thickness.